1. Field of the Invention
The present invention relates to a cold-cathode type of electron-emitting device. The present invention also relates to an electron beam-generating apparatus, and an image-forming apparatus employing the electron-emitting device.
2. Related Background Art
Cold cathode devices are known as devices capable of emitting electrons with a simple structure. For example, a cold cathode device is reported by M. I. Elinson (Radio Eng. Electron Phys., vol. 10, pp. 1290-1296 (1965)). These devices are based on the phenomenon that electrons are emitted by flowing electric current in parallel through a thin film of small area formed on a substrate. Such devices are called generally surface-conduction type electron-emitting devices. The surface-conduction type electron-emitting devices include the ones using a thin SnO2(Sb) film developed by M. I. Elinson as mentioned above; the ones using a thin Au film (G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, vol. 9, p. 317, (1972)); and the ones using a thin ITO film (M. Hartwell and C. G. Fonstad: IEEE Trans. ED Conf., p. 519 (1975)).
A typical construction of the surface conduction type electron-emitting device is shown in FIG. 30. This device comprises electrodes 82, 83 for electric connection, a thin film 85 formed from an electron-emitting material, a substrate (insulating base) 81, and an electron-emitting portion 84. Conventionally, in such a surface conduction type electron-emitting device, the electron-emitting portion is formed by electric current-heating treatment called xe2x80x9cformingxe2x80x9d. In this treatment, electric voltage is applied between the electrode 82 and the electrode 83 to flow electric current through the thin film 85 and to destroy, deform, or denature locally the thin film 85 by utilizing Joule heat generated. Thereby, the electron-emitting portion 84 which has high electric resistance is formed, thus the function of electron emission being obtained. Here the state of the high electric resistance results from discontinuity of the thin film 85 in which cracks of 0.5 to 5 xcexcm long are formed locally and the cracks have an island structure therein. The island structure means a state of the film that the film contains fine particles of several tens of angstroms to several microns in diameter and the particles are discontinuous but the film is electrically continuous. In conventional surface conduction type electron-emitting device, voltage is applied to the aforementioned discontinuous high-resistance film through the electrodes 82, 83 to flow current at the surface of the device, thereby electron are emitted from the fine particles.
A novel surface conduction type electron-emitting device in which electron-emitting fine particles are distributed between electrode was disclosed by the inventors of the present invention in Japanese Patent Application Laid-Open Nos. Hei-1-200532 and Hei-2-56822. This electron-emitting device has advantages that (1) high electron-emitting efficiency can be obtained, (2) the device can be readily prepared because of its simple construction, (3) many devices can be arranged on one and the same substrate, and so forth. FIG. 31 shows a typical construction of such a surface conduction type electron-emitting device, which comprises electrodes 82, 83 for electric connection, an electron-emitting portion 86 having electron-emitting fine particles dispersed therein, and a substrate 81.
In recent years, attempts are made to use the aforementioned surface conduction type electron-emitting device for an image-forming apparatus. One example is shown in FIG. 32, which illustrates an image-forming apparatus having a number of the aforementioned electron-emitting devices arranged therein. The apparatus comprises wiring electrodes 92, 93, electron-emitting portions 94, grid electrodes 95, electron-passing holes 96, and an image-forming member 97. This image-forming member is made of a material such as fluorescent materials and resist materials which causes light-emission, color change, electrification, denaturing or like change on collision of electrons. With this image-forming apparatus, the linear electron sources having a plurality of electron-emitting portions 94 arranged between the electrodes 92, 93, and grid electrodes 95 are driven in XY matrix, and electrons are made to collide against the image-forming member 97 in correspondence with information signals to form an image.
The electric characteristics (current-voltage characteristics) of conventional surface conduction type of electron-emitting devices are explained by reference to FIG. 6. In conventional electron-emitting devices, electron emission increases rapidly from a certain device voltage Ve (voltage applied to the device) with increase of the device voltage, and at a device voltage Vd, a sufficient electron beam is emitted: for example, a sufficient electron beam for forming an image in the above-mentioned image-forming apparatus. The device current If (current which flows in the device) increases with the device voltage, and the rate of the increase becomes larger at around the device voltage Ve. In such conventional devices generally, strong ineffective current, which is useless for electron emission, flows as shown in FIG. 6. The ratio of the ineffective current to the device current If rises in some cases to as much as about 50%. Such increase of the ineffective current will cause increase of power consumption in driving the electron-emitting device, and increase of heat generation in the electron-emitting device to deteriorate electron-emitting characteristics (electron-emission efficiency, electron-emission stability, etc. Further the increase of the ineffective current gives rise to the problems, when the electron-emitting device in which the ineffective current is great is used for an image-forming apparatus: 1) the ineffective current flows to wiring electrodes to cause voltage drop, whereby the quantity of electron emission varies with the electron-emitting devices, and 2) the ineffective current varies depending on the kind of the image (namely, difference in inputted information signal) to cause voltage drop in wiring electrode, whereby quantity of the emitted electrons varies. Such disadvantageous phenomena further cause lowering of contrast and sharpness of the formed image; and in particular, in the case where the formed image is a fluorescent image, bring about variation and change of luminance of the fluorescent images, which makes it difficult to obtain image finess and to enlarge a picture screen, and further increase the power consumption.
An object of the present invention is to provide an electron-emitting device and an electron beam-generating apparatus in which ineffective current is extremely weak.
Another object of the present invention is to provide an electron-emitting device and an electron beam-generating apparatus which are excellent in electron emission characteristics such as electron-emission efficiency, and electron-emission stability, and which consumes less electric power.
A further object of the present invention is to provide an electron beam-generating apparatus in which ineffective current is extremely weak in a whole apparatus, and which gives an image with high contrast and high sharpness with less power consumption, in particular an electron beam-generating apparatus capable of forming a luminescent image with extremely low variation and low fluctuation of luminance.
According to an aspect of the present invention, there is provided an electron-emitting device having an electron-emitting region between electrodes on a substrate, the electron-emitting region containing fine particles dispersed therein at an areal occupation ratio of the fine particles ranging from 20% to 75% of the electron emitting region.
According to another aspect of the present invention, there is provided an electron-emitting device having an electron-emitting region between electrodes on a substrate, the electron-emitting region containing the fine particles dispersed therein at gaps of from 5 xc3x85 to 100 xc3x85 and having average particle diameter of from 5 xc3x85 to 1000 xc3x85.
According to still another aspect of the present invention, there is provided an electron-emitting device having an electron-emitting region between electrodes on a substrate, the electron-emitting region containing fine particles dispersed therein at an areal occupation ratio of the fine particles ranging from 20% to 75% of the electron-emitting region, and the fine particles being dispersed at gaps of from 5 xc3x85 to 100 xc3x85 and having average particle diameter of from 5 xc3x85 to 1000 xc3x85.
According to a further aspect of the present invention, there is provided an electron-emitting device having an electron-emitting region between electrodes on a substrate, the voltage application length in the electron-emitting region ranging from 5 xc3x85 to 300 xc3x85.
According to a still further aspect of the present invention, there is provided an electron-emitting device having an electron-emitting region between electrodes on a substrate, the electric field strength in the electron-emitting region being not less than 107 V/cm.
According to a further aspect of the present invention, there is provided an electron-beam generating apparatus, comprising a plurality of the above-specified electron-emitting devices and a modulation means for modulating the electron beams emitted from the electron-emitting devices in accordance with information signals.
According to a still further aspect of the present invention, there is provided an image-forming apparatus, comprising a plurality of the above-specified electron-emitting devices, a modulation means for modulating the electron beams emitted from the electron-emitting devices in accordance with information signals, and an image-forming member for forming image on irradiation of electron beams.
According to a further aspect of the present invention, there is provided an image-forming apparatus, comprising a plurality of the above-specified electron-emitting devices, a modulation means for modulating the electron beams emitted from the electron-emitting devices in accordance with information signals, and a light-emitting member for emitting light on irradiation of electron beams.
According to a still further aspect of the present invention, there is provided an image-forming apparatus, comprising a plurality of the above-specified electron-emitting devices, a modulation means for modulating the electron beams emitted from the electron-emitting devices in accordance with information signals, a light-emitting member for emitting light on irradiation of electron beams, and a recording member for recording an image on irradiation of light from the light-emitting member.
According to a further aspect of the present invention, there is provided an image-forming apparatus, comprising a plurality of the above-specified electron-emitting devices, a modulation means for modulating the electron beams emitted from the electron-emitting devices in accordance with information signals, a light-emitting member for emitting light by irradiation of electron beams, and a supporting means for a recording member for recording an image by irradiation of light from the light-emitting member.